1. Field
The following description relates to a method of manufacturing a thin-film transistor having an active layer that includes an oxide semiconductor, a method of manufacturing an organic light-emitting display device including the same, and a thin-film transistor and an organic light-emitting display device manufactured using the methods.
2. Description of the Related Art
A flat display device, such as an organic light-emitting display device, a liquid crystal display device, or the like, is manufactured on a substrate on which at least one thin-film transistor, at least one capacitor, and the like for driving the flat display device and a pattern including wirings for connecting the thin-film transistor, the capacitor, and the like are formed. The thin-film transistor includes an active layer for providing a channel region, a source region, and a drain region. A gate electrode is formed on the channel region and electrically insulated from the active layer by an insulation film.
The active layer of the thin-film transistor is usually formed of a semiconductor material, such as amorphous silicon or poly-silicon. When the active layer is formed of amorphous silicon, it is difficult to implement a driving circuit operating at a high speed since mobility of charges is low, and when the active layer is formed of poly-silicon, mobility is high, but an additional compensation circuit is necessary since a threshold voltage is not uniform. In addition, since a comparable method of manufacturing a thin-film transistor by using low temperature poly-silicon (LTPS) includes an expensive process, such as a laser annealing process, facility investment and management costs are high, and it is difficult to apply the comparable method to a large-area substrate. To solve these problems, research using an oxide semiconductor as an active layer has recently been conducted.
An organic light-emitting display device using an oxide semiconductor has an offset of a set or predetermined interval for an insulation characteristic between a gate electrode and a source/drain wiring in a top gate structure. With this offset, an increase in a resistance at both ends of a source/drain causes a problem of a decrease in a current characteristic of a thin-film transistor. In existing silicon semiconductors using an LTPS process, although an ohmic contact layer is formed by a high-density doped semiconductor as a method for solving this problem, since there are no high-density doping methods for an oxide semiconductor, a method of increasing the carrier density of an active layer through plasma treatment is used, but this method also needs an additional mask process.